This is the 133rd most frequent Russian word.
силы
"Силы" in English means "forces" or "strength."
The word 'силы' (plural of 'сила') here refers to 'strength' or 'efforts'.
Она приложила все свои силы, чтобы достичь этой цели.
She put all her strength into achieving this goal.
The word 'сил' (genitive plural of 'сила') indicates 'strength' or 'energy' in a possessive form, often used for physical endurance.
После долгого пути у меня не осталось сил.
After the long journey, I had no strength left.
The word 'силы' means 'forces' here, referring to natural phenomena like wind or gravity.